1) Field of the Invention
The invention relates to a valve for controlling the flow of fluids and, more particularly, to a sequencing valve for controlling the flow of fluids from multiple fluid circuits through one or more ports, for example, to a device such as a heat exchanger.
2) Description of Related Art
Secondary refrigeration systems, sometimes referred to as hydronic systems, provide heated and chilled fluids to a terminal unit, which uses the fluids to heat or cool air. A conventional terminal unit includes two heat exchangers, one that receives the hot fluid for heating the air, and one that receives the cold fluid for cooling the air. The flow of the fluids, usually water, is controlled by thermostatically operated valves known as automatic temperature control (ATC) valves. In a heating mode of operation, a first set of valves opens to fluidly connect the first heat exchanger to a hot water supply and a return line so that the water flows from the hot water supply, through the heat exchanger where thermal energy is transferred to the air, and to the hot water return line for reheating or discharging. In a cooling mode of operation, the first set of valves closes the connections between the first heat exchanger and the hot water supply and return lines. A second set of valves opens to fluidly connect the second heat exchanger to a cold water supply and a return line. The cold water then flows from the cold water supply, through the second heat exchanger where thermal energy is absorbed by the water from the air, and to the cold water return line for re-cooling or discharging. Thus, the terminal unit of the conventional system includes separate fluid circuits for heating and cooling, each circuit having its own heat exchanger and control valves. In addition, each fluid circuit can separately be provided with devices for monitoring and regulating the fluid flow. The duplication of the components in the separate fluid circuits increases the initial cost of the refrigeration system as well as the size and complexity of the system.
Thus, there exists a need for a hydronic system and sequencing valve that reduce the number of duplicate components required for the separate heating and cooling fluid circuits described above. The system should be capable of operating in multiple modes to selectively heat or cool the air in the terminal unit.